Host susceptibility and microclimatic conditions influencing the development of blight diseases caused by Calonectria henricotiae

Boxwood blight caused by Calonectria pseudonaviculata or Calonectria henricotiae is the major disease affecting boxwood (Buxus sp.). Other members of the Buxaceae family, Pachysandra and Sarcococca can also be infected. The trials reported here were conducted to test the susceptibility of Pachysandra terminalis ‘Compacta’ and Sarcococca confusa to this pathogen. The susceptibility of both species was compared to three different taxa of boxwood plants, representing three different levels of susceptibility to the pathogen: from the most susceptible Buxus sempervirens ‘Suffruticosa’ via the intermediate Buxus sempervirens var. arborescens to the most tolerant Buxus microphylla ‘Herrenhausen’. The experiments took place under in greenhouses and outside in a container field. Plants were artificially inoculated with AT01, further determined as a strain of Calonectria henricotiae. The progress of the disease was continuously monitored and parameters such as leafspotting, lesions and leaf drop were evaluated. Results show that the level of susceptibility of Pachysandra terminalis ‘Compacta’ to Calonectria henricotiae is low to moderate and comparable to the susceptibility of Buxus microphylla ‘Herrenhausen’ or, depending on the conditions, Buxus sempervirens var. arborescens. In our trial, Sarcococca confusa did not produce any symptoms of a disease caused by Calonectria henricotiae.